Cathode ray tube



May 13 1969 sATosHl SHIMADA ErAL 3444'421 CATHODE RAY TUBE Filed Deo. 29, 1966 iup HTTO/QA/Ey May 13, 1969 Filed Deo. 29, 1966 CATHODE RAY TUBE iEiS.

sATosHl SHIMADA ET AL U.S. Cl. 315-21 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to a cathode ray tube of the type having a single gun and a post acceleration and focusing tube, and more particularly to such a cathode ray tube which has provided therewith an improved color switching device which includes two pairs Vof electrodes which are provided on opposite sides of the outer surfaces of the neck portion of the cathode ray tube, and two pairs of inner electrodes which are made of a low resistance material and which are located in positions corresponding to the outer electrodes. A layer of high resistance material is provided around the inner electrodes. The color switching is accomplished by applying switching signals in opposite directions to the two pairs of outer electrodes.

Background of the invention This invention is particularly directed to improvements in color picture tubes of the type in which an electron lbeam is deflected through the use of two electrostatic fields, the purpose of the deection being to alter the incidence angle of the electron beam to the grid in order to accomplish color switching. It is well known by those skilled in this art that color switching is effected by defiecting an electron beam with a magnetic field in order to change the incidence angle of the electron beam to the grid. It is also well known that an electron beam is electrostatically deected in a monochrome tube. When a magnetic eld is utilized for such a purpose, however, it requires the utilization of large power and results in extensive unwanted radiation. In addition, this method of deflection can be employed for a line sequential color television system but cannot be employed for a dot sequential system. In view of this fact those skilled in the art have considered that color switching can be effected by conventional electrostatic deflection rather than by the use of a magnetic eld. The utilization of conventional electrostatic deliection, however, also results in various problems such as the provision of the power source for Summary of the invention In view of the foregoing the primary object of the present invention is to provide a one-gun color picture tube in which electrodes are provided on the outer and inner surfaces of the neck portion of the cathode ray tube and in which the electron beam is deflected through the 3,444,421 Patented May 13, 1969 ice utilization of low power in order to provide color switching.

Another object of the present invention is to provide a one-gun color picture tube with a simplified one-gun color demodulator circuit.

Still another object of the present invention is to provide a one-gun color picture tube which minimizes color distortion and unnecessary radiation and which is thereby ystable in operation.

These and further objects, features and advantages of the present invention will appear from the following detailed description of a preferred embodiment of the invention which is to be read in conjunction with the accompanying drawings in which like components of the Several views are identified by the same reference mumeral.

Brief description of the drawings FIG. l is a schematic diagram in block form illustrating one example of a cathode ray tube of the present invention as applied to a color television picture tube;

FIG. 2 is an enlarged view of a portion of FIG. 1 and illustrating the principal parts of the present invention;

FIG. 3 is a cross section taken on the line 3--3 of FIG. 2;

FIG. 4 is an electrical equivalent circuit diagram of the principal components illustrated in FIG. 2; and

FIG. 5 is a wave form representative of a color switching signal.

Description of the preferred embodiment Referring now to the drawings and particularly to FIG. 1, the reference numeral 11 indicates an antenna and the reference numeral 12 indicates a color signal transmission system from which are obtained a luminance signal Y, a chrominance signal CS which is demodulated from a subcarrier, and horizontal and vertical synchronizing pulses which are identified respectively as PH and Pv. The color cathode ray tube is identified by the numeral 13. The cathode ray tube 13 is so designed that its electron gun 14 is supplied with a low-frequency component of a luminance signal which is identified as YL. This low-frequency component YL is supplied by the amplifier 15 and has a value of for example 0 to 2 mc. The electron gun 14 is also supplied with a high frequency component YH of a luminance signal which varies from 2 to 4 mc. and the chrominance signal CS, these components being supplied by the amplifier 16.

The chrominance CS is fed to a color burst signal separator 17 to which is also applied one portion of the output from the horizontal deflection circuit 18. The horizontal deection circuit 18 has applied thereto the horizontal synchronizing signal PH which selects the color burst signal. The output of the color burst signal separator 17 is fed to a color switching signal generator 25 from which is obtained a sinusoidal signal fs of 3.5 8 mc. The signal fs is applied to the outer electrodes 19b and 20a of the cathode ray tube 13. In addition, one portion of the sinusoidal signal fs is fed to a multiplier 21 from which is obtained a sinusoidal signal 2j"s of 7.16 mc. which is applied to the outer electrodes 19a and 20b, Further, one portion of the sinusoidal signal fs of 3.58 mc. is fed to a key-out signal generator 22. A key-out signal of 10.7 rnc. is obtained from the key-out signal generator 22 and is applied to the electron gun 14 after first being superimposed on the low-frequency component YL of the luminance signal Y which has been transmitted from the arnplifier 15. In addition, the deflection yoke 24 is supplied with the outputs from the horizontal deflection circuit 18 and the vertical output circuit 23.

The color cathode ray tube 13 includes a color phosphorous screen 26 which is composed of red, green and blue phosphorous strips which are identified respectively by the designations R, G and B. These phosphorous strips extend vertically across the face of the tube 26 and are sequentially arranged in a repeating cyclic order which, for example, may be red, green, blue, red, etc. Adjacent the color phosphorous screen 26 and within the tube 13 there is provided a color selection grid 27 which is composed of many grid wires 27a. The grid wires 27a are positioned opposite the lines of demarcation between the green and blue phosphorous strips G and B and extend parallel to these phosphorous strips throughout their length. The electron beam 28 emanating from the electron gun 14 is caused to always impinge upon the red phosphor strips R and the color selection grid 27 is supplied with a potential which is lower than the potential applied to the color phosphor screen 26. In addition, the inner surface of the conical portion 13a of the tube 13 is coated with a high voltage conductive layer 29 to which a high potential is applied.

In accordance with the present invention two pairs of electrodes 19a, and 19b and 20a, 2Gb are mounted on the neck portion of the cathode ray tube 13. These electrodes as illustrated in FIG. 1 are mounted in front of and to the rear of the deflection yoke 14, i.e., at opposite ends of the deflection yoke .14. The electrodes of each pair are also disposed opposite in a direction perpendicular to the longitudinal direction of the phosphor strips R, G, B, etc. The electrodes may be disposed in close proximity to the deflection yoke 14 or they may partly underlie the deflection yoke 14. The electrodes are formed by vapor depositing a coating of, for example, a conductive material. It is preferred that the electrodes a and 20b which are located in front of the deection yoke 14 partly extend over the conical portion 13a of the tube 13.

A layer of low resistance material is provided on the inner surface of the neck portion of the cathode ray tube 13 at those locations corresponding to the electrodes 19a, 19b and 20a, 20b. These low resistance layers are identified respectively as 46a, 46b, 47a and 47b. The area around these low resistance layers is coated with a high resistance layer 30 which has a resistance value which will be hereinafter described. One end of the high resistance layer 30 is grounded in AC current. It is preferred that the area of each low resistance layer 46a, 46b, 47a and 47b be of greater than the corresponding area of each of the electrodes 19a, 19b and 20a, 20b. In the embodiment illustrated in the drawings the high resistance layer 30 is formed around the 10W resistance layers 46a, 46b, 47a and 47b and on the inner surfaces of the conical portion 13a and on the neck portion 13b of the cathode ray tube 13 between the high voltage conductive layer 29 and the electron gun 14. In addition grooves 31 are formed in the high resistance layer 30, the grooves 31 extending parallel to the tube axis. The grooves 31 are utilized to apply a high voltage to the electron gun 14 from the high voltage conductive layer 29. For this purpose there is provided in each groove 31 a conductor 32 and the ends of the conductor 32 are joined to the high voltage conductive layer 29 and to the electron gun 14 respectively. One end of the high resistance layer 30 is grounded through the high voltage conductive layer 29 in the AC circuit. It is preferred that the conductors 32 be disposed at locations corresponding to the intermediate portions between the electrodes 19a and 19b.

As previously described, the color switching signals are applied to the outer electrodes 19a, 19b, 20a and 20b. For this purpose the output terminal of the color switching signal generator is connected between the electrode 19b and ground, while the output of the lmultiplier 21 which produces the signal 2fs is connected between the other outer electrode 19a and ground. In a similar manner the output side of the color switching generator 25 and of the multiplier 21 are connected respectively to the other pair of outer electrodes 20a and 2Gb, but the connections are in opposing relationship to the connections made to the electrodes 19a and 19b. In other words, the relationship is such that when the output side of the color switching generator 25 is connected to the electrode 19b it is also connected to the electrode 20a. In addition, a shield plate 34 is disposed on the outside of the outer electrodes 19a, 19b, 20a and 20b through an insulating layer.

In the color cathode ray tube described above, electrostatic capacitances 35a and 35b are established between the electrodes 19a and 19b as illustrated in FIG. 4. An electrostatic capacitance 36 is also formed between the adjacent layers 46a and 46b on the inside of the neck portion 13b of the cathode ray tube 13 since the layer 30 has a high resistance value. These capacitances 35a, 3512 and 36 are equivalent to being connected together in a series as illustrated inY FIG. 4. Moreover, since the end of the high resistance layer 30 is grounded in AC current, the connecting points between the capacitances 35a and 36 or between the capacitances 35b and 36 are grounded through leakage resistors 37a and 37b of the high resistance layers in AC current. The reference numerals 38a, 38b, 39a and 39b designate the capacitances formed between the electrodes 19a, 19b, 20a and 20h and the shield plate 34. The reference numerals 48a, 48b, 49a and 49b designate the capacitances formed between the low resistance electrodes 46a, 4Gb, 47a and 47b and the shield plate 34. This means that the color switching generator 25 is connected between one end 40b of the series capacitances and the ground, and that the multiplier 21 is connected between the other end 40a and the ground. In this case, the output sides of the circuits 25 and 21 and the capacitances 38b and 38a respectively are connected in parallel and are adapted to function in parallel resonance with respect to the signals fs and 215 respectively.

The resistance value of the high resistance layer 30 is so selected that the time constant which is dependent upon the resistance value of the leakage resistances 37a and 37b and upon the capacitance value of the capacitances 35a or 35h is greater than the period of the color switching signal fs. Since the distance between the electrodes of the capacitances 35a or 35]; is shorter than that of the capacitance 36, and the dielectric constant between these electrodes is greater than that of the capacitor 36, the capacitance value of the capacitances 35a or 35b is remarkably greater than that of the capacitor 36. Accordingly, the signal fs is applied lbetween the terminals 40a and 40b, namely between the electrodes 19a and 19b, and almost all of its signal voltage is concentrated on the capacitor 36. That is, an electrostatic eld of the signal fs is produced in the neck portion 13b of the cathode ray tube 13 corresponding to the portion between the electrodes 19a and 19b. In a similar manner an electrostatic eld of the signal 2fs is provided in the tube 13. These electrostatic elds are so composed as to produce a color switching electrostatic eld 41 as illustrated in FIG. 5, the field 41 varying with the lapse of time.

In a similar manner a color Switching electrostatic eld 42 is formed between the low resistance layers 47a and 47b in the cathode ray tube 13 by the signals applied to electrodes 20a and 20b. This electrostatic eld 42 is in opposite phase to that established by the electrodes 19a and 19b. In FIG. 4 the reference numerals 43a and 43b indicate the capacitances established by the electrodes 20a and 20b and the low resistance layers 47a and 47b. The reference numeral 44 designates a capacitor produced between the low resistance layers 47a and 47b and the numeral 45 identifies the leakage resistance between these capacitors.

Since the electrostatic fields are produced in the cathode ray tube 13 in the manner described above and the electron beam 28 is not deflected by the outer electrodes 19a, 19b, 20a and 20b at the zero portion 41R of the color switching signal 31, the electron `beam impinges upon the red phosphor strip R as previously described.

In a similar manner when the color switching signal approaches its negative peak value 41G the electrode 19h becomes negative, the electron beam 28 is diverged on the side of the electrode 19a and is then converged on the side of the electrode 20b, thereafter impinging upon the green phosphor strip G adjacent the red phosphor strip R. When the color switching signal 41 approaches its positive peak value 41B, the electron beam 28 is diverged and is then converged in directions opposite to those in the foregoing, with the result that it irnpinges upon the green phosphor strip G. In this manner the electron beam is electrostatically detlected by the color switching signals, and the color switching signal is synchronized with the chrominance signal fed to the electron gun 14 so that a color picture is reproduced on the color phosphor screen 16.

Where the capacitance values of the capacitors 35a and 35b are for example 100 pf., and the resistance value of the leak resistances 37a and 37b are l0 MQ, their time constant is one millisecond. This time constant is sufficiently greater than the period of the colol switching signal when color reproduction is achieved in a dot-sequential manner. Accordingly, this invention is applicable not only to dot-sequential color reproduction but is also applicable to line-sequential color reproduction at a frequency of 5.25 kc. lower than 3.58 mc. The resistance value of the high resistance layer 30 is so selected that the charges stored on the inner wall of the tube 13 by the secondary electrons produced in the tube may be evolved through the layer 30. Therefore, when a beam current from the electron gun is approximately 30G/ta., if secondary electrons in the order of SOpa., which is about 1/6 of the current, are emitted from the color selection grid 27, and some secondary electrons of approximately 20,ua., which is about j/M of SOpa. reaches the high resistance layer 30, the secondary electrons flow to the ground through one of the leakage resistors 37a or 37b. The voltage drop in each leakage resistor 37a or 37b is such that when its resistance value is approximately MS2, the voltage drop is 10aa. times 10 MQ, or 100 v. This is smaller than the peak value of about 1.5 kvpp. of the color switching signal 41, so that if the leakage resistanees 37a and 37b have a value in the range of 1 to 10 MS2, a color switching electrostatic eld is established in the tube and the potential distribution in the tube is not disturbed. The high resistance layer 30 can be formed by vapor deposition of, for example, chromium oxide.

In the case Where the peak value of the color switching signal is 1.5 kvpp., which can be obtained by selecting the deection angle at the neck portion 13b to be about 128', and the capacitance values of the capacitances 35a and 35b are 50 pf., the reactive power from a color switching signal of 3.58 mc. that passes through the two capacitors 35a and 35b is approximately 315 w. Where the inductance of a coil connected to both ends of the series capacitors is about 40gb., and the coil is adapted to resonate with the color switching signals and its Q is about 120, the power of color switching signal is 2.5 w. In practice, the value of the capacitors 35a and 35b can be made smaller, and therefore the deflection power can also be decreased. However, since the value of capacitance 38a, 38b, 39a and 39b to the shield plate 34 are approximately 30 to 200 pf., the deflection power is selected in the range of 3 to 10 w. in practice.

In a chromatron tube 13 having a color grid 27 disposed opposite to the color phosphor screen 26, the capacitance of the grid is about 2.000 pf., the color switching signal is about 400 vpp., the reactive power is approximately 2000 w. and the deection is about 25 w. (in the case where Q is 80). These values are about four and ten times as great as those of the cathode ray tube of the present invention. In addition, it is considered that color switching is electromagnetically effected in the vicinity of the neck portion. In this case, the capacitance of the resonance circuit including the deection is about 700/4f., the color switching signal is about 700 vvp., the reactive power is 1000 w. and the deflection power is approximately 11 w. (in the case where Q equals 90). These values are about 3.5 and 4.5 times as great as those of the cathode ray tube of the present invention.

It can accordingly be seen from the foregoing that the present invention requires an extremely low power for color switching. In addition, the construction of the color switching device is very simple as can be seen from the drawings. Furthermore, the distance of the grid wires 27a from the color selection grid 27 corresponds to the width of three phosphor strips and this distance is greater than that in conventional chromatron tubes. This invention does not necessitate connection of every other grid wire 27a and insulation of -adjacent ones, and therefore enables relatively simple manufacture of the cathode ray tube. Moreover, the number of the phosphor strips constituting the picture element between adjacent grid wires 27a is great so that a picture can be reproduced with high resolution.

In the present invention the color switching frequency can be as high as 3.58 mc., but the deflection power required is small as described above. This enables electron beam deection to be accomplished through the use of relatively small power by a color switching signal such that the signal 215 of the multiplied frequency is superimposed on the signal fs. The period that the electron beam stays on each phosphor is lengthened as illustrated in FIG. 5, and the period of the electron beam moving from one phosphor strip is shortened. Therefore, the use of such a color switching signal provides a color cathode ray tube which is free from color distortion and which is stable in operation. In addition, in the present example the signals fs and 2fs can be applied separately between either one of the electrodes 19a and 19b and ground, and the capacitors 38a and 38h between the electrodes 19a and 19b and shield plate 34 are each utilized as one element of the residence circuit of the signal supply circuit. The shield plate 34 can be used as one element of the input circuit of the color switching circuit as well as serving to prevent the color switching signal from radiating to the outside. In such a case, it is considered practical to apply the signals fs and 2fs in series between either one of the electrodes and the ground. In the present case, even if either one of the capacitors 38a and 38h is employed as one input circuit of the signal, another capacitor element is required at the other input circuit. In the cathode ray tube of the present invention, however, such a capacitance element is not required.

In the prior art it is considered that in order to accomplish color switching electrostatically a color switching deflection plate is disposed in the cathode ray tube in the same manner as an electrostatic deection plate is disposed in a usual electrostatic deection type cathode ray tube. In this case, however, a deection voltage supply lead must be led outside of the tube and the same high potential as that applied to the high voltage conductive layer 29 must be fed to the color switching deflection plate in order to insure that the potential of the electron beam path is not disturbed by the insertion of the color switching dellection plate. Therefore, attention must be paid to insulating the lead for deflection AC voltage application and for high voltage application. This makes it diflicult to maintain the deflection yoke in position, and the insertion of the color switching deflection plate is impossible. In the cathode ray tube of the present invention, however, electrodes 19a, 19b and 20a and 20b are supplied with only the color switching signal and are grounded in DC current, so that the difficut insulation problem illustrated above is not required. In addition, with only the electrodes 19a, 19b, 20a and 20h provided on the outside of the tube, such an adverse influence is occasioned on the inner surface of the neck portion 13b that it is charged with secondary electrons to such an extent as to change the potential of the electron beam path, thereby deteriorating focusing of the electron beam. In order to avoid this, the high voltage conductive layer 29 is extended on the inner surface of neck portion 13b at places corresponding to the electrodes 19a, 19b, 20a and 20b. The high voltage conductive layer 29 is grounded in AC current so that no color switching field is produced.

In the cathode ray tube of the present invention the low resistance layers 46a, 46h, 47a and 47b are provided in the neck portion 13b at places opposite to the electrodes 19a, 19b, 20a and 20b, and the high resistance layer 30 is provided at the places around the low resistance layers 46a, 46b, 47a and 47b, and their resistance values are selected as described above. As a result of this, a color switching eld can be established in the cathode ray tube without any diiculty and the inner surface of the tube has a DC potential. That is, there is no possibility that the potential of the electron beam' path varies to deteriorate focusing of the electron beam. In addition with the conductors 32 formed in the grooves 31 in the high resistance layer 30, a high voltage can be applied with a low resistance from the high voltage conductive layer 29 through the conductors 32 to the electron gun 14.

In the foregoing, the signal 2fs is superimposed on the signal fs but color switching can be carried out iby superimposing a signal 3fs having a frequency which is three times as high as the signal fs. In some cases color Switching may be effected by the signal fs only and in such event the signal fs can be applied to the electrodes 19a and 19b in opposed phase relationship.

It will be apparent to those skilled in the art that although a preferred embodiment of the invention has been described and illustrated, that many modilications and variations may be made thereto without departing from the the scope of the novel concepts of this invention as set forth in the appended claims.

We claim:

1. A cathode ray tube for producing color-images wherein color switching is accomplished by low power electrostatic fields, said cathode ray tube comprising an elongated neck portion having mounted therein an electron beam gun, one end of said neck portion opening into an enlarged sealed chamber, the end of said chamber opposite said gun consisting of a color phosphor screen upon which said electron beam generated by said gun impinges, a post acceleration and focusing grid within said chamber and opposite said color phosphor screen, said screen being made up of alternating phosphor strips of three primary colors on one of which said electron beam is normally focused through said grid, first and second pairs of electrodes mounted at spaced positions on the outer surface of said neck portion with the electrodes of each pair being mounted opposite each other, first and second switching means for applying alternating current deflection voltages to said first and second pairs of electrodes, respectively, whereby an electrostatic deflection field is established between each of said pairs of electrodes for selectively deflecting said electron beam from said phosphor strips of said one color to the phosphor strips of the other two primary colors, a layer of low resistance material coated on the inner surface of said neck portion at positions thereof corresponding to the locations of said first and second pairs of electrodes, and a layer of high resistance mateterial coated on the inner surface of said neck portions contiguous to and encompassing said layers of low resistance material.

2. A cathode ray tube in accordance with claim 1 wherein the ends of said high resistance layer are grounded in AC current.

3. A cathode ray tube in accordance with claim 2 wherein a deflection yoke surrounds said neck portion, and said first and second pairs of electrodes being mounted on said neck portion at opposite ends of said yoke.

4. A cathode ray tube in accordance with claim 3 wherein said deflection voltages applied to said first and second pairs of electrodes are in opposed relationship to thereby change the incidence angle of said electron beam with respect to said post acceleration and focusing grid.

5. A cathode ray tube in accordance with claim 4 Wherein said first and second pairs of electrodes are grounded in DC current.

6. A cathode ray tube in accordance with claim 5 wherein a shield plate is mounted on said neck portion to surround and shield said electrodes.

References Cited UNITED STATES PATENTS 2,672,575 3/1954 Werentels 315-21 2,803,781 8/1957 Jurgens 315-21 X 2,864,032 12/1958 Arndursky et al. 315-21 X 2,938,142 5/1960 Oestreicher 315-21 X 2,959,483 11/1960 Kaplan 315-21 X 2,961,576 11/1960 Burgett 315-21 3,147,340 9/1964 Ehrich 315-21 X RODNEY D. BENNETT, JR, Primary Examiner.

BRIAN L. RIBANDO, Assistant Examiner. 

